Roofing and the like



Patonted June 3, 1941 ROOFING AND THE LIKE Richard a. Wilkins, Rome, N.Y., assignor to Revere Copper and Brass lnofl 'l rated, Rome, N. Y., acorporation of Maryland No Drawing. Application March 4, 1941.

Serial No. 381,697 4 2Claims.- (circa-mo) My invention relates toroofing and the like, and particularly to improvements in the roofingforming the subject matter of my pending application Serial Number363,515, filed October 30, 1940.

As pointed out. in the above mentioned pending application. the materialheretfore commonly employed for copper roofing. sheathing, and otherexposed protective coverings for buildings has been thin rolled sheetsof highly refined copper. Further, in refining copper for these purposesit has heretofore always been the practice of producers thereof toremove so far as possible all impurities so as to secure as pure acopper as possible. The known high resistance of pure copper generallyto chemical corrosion, and the observed fact that impurities commonlyfound in rolled copper tend to make it less ductile in both the hot andcold rolled conditions, more difllcult to produce by either hot orcoldrolling, and commonly cold short in the sense that it tends to crackwhen bent or otherwise cold worked, have caused pure copper heretoforeto be considered the most satisfactory commercially available materialfor light weight metal roofing and the like. In fact during the pastforty years copper roofing has for these reasons been made almostexclusively of electrolytically refined copper, which commonly is 99.9%pure copper.

Nevertheless it is a frequently observed fact that copper roofing. evenwhen substantially 100% pure electrolytically refined copper, oftenfails in use, being subject to cracking sufiicient to render itnon-waterproof. Heretoforeit was believed that these cracks were causedby mechanical fatigue resulting by reason of the cyclic stresses set upby alternate expansion and contraction of the copper sheets undervarying temperature conditions. For that reason builders heretofore haveresorted to expensive roof constructions, and various expensiveexpedients such as corrugating the roofing and the employment ofelaborately designed expansion joints, and theuse of heavy gauge copperin the attempt to relieve or reduce the effect on the roofing of thesecyclic stresses and thereby eliminate so far as possible this form offailure. Although these attempts have been partially successful, theexpense incidental thereto, and themany failures which actually haveoccurred in spite of these precautions, have seriously interfered withthe general adoption of this otherwise very satisfactory roofing.

, As pointed out in applicant's pending applicopper cation abovereferred to, applicant has found that the failure of copper roofing andthe like heretofore has not been correctly understood. This material, hehas found, does not fail primarily by reason of the cyclic stresses towhich it is subjected when in use, as heretofore believed, but,strangely enough, primarily by reason of a heretofore wholly unsuspectedtype of corrosion which occurs when this highly pure copper is exposedto an atmosphere contaminated by wind borne products of combustion ofmodern domestic and industrial fuel burning appliances and industrialatmospheres in general.

Applicant has found, that upon removing the patina and other accumulatedcorrosion products from copper roofing which has failed, the

roofing surface thus exposed is characteristically pitted, instead ofbeing .in its smooth unpitted condition in which it originally left therolling mill or the metal showing a uniform decrease in thickness overits whole surface due to corrosion.

His investigations show that these pits are caused by the formation onthe copper, when exposed to a contaminated atmosphere, of a film ofcorrosion products which is characterized by a lack of adhesionto thecopper, a lack of tenacity in respect to failure, and a tendency towardperviousness which allow the copper to be attacked locally rather thanuniformly by the corrosive media and thereby result in the formation ofsharply defined, inwardly pointed pits in the nature of notches. He hasfound that copper so attacked rapidly fails when subjected to the cyclicstresses hereinbefore referred to by reason of the natural tendency ofthe stresses to be concentrated in the metal below the bottoms of thenotch-like pits. As a result of this concentration of the stresses, themetal below the bottoms of the pits work hardens" and the fatiguestrength of the material is exceeded, and as a result the metal cracksat the pits.

Pure copper roofing applicant has found is comparatively sensitive tothis notch effect," when caused by a combination of chemical corrosionand subjection to cyclic stresses, on account of the film which forms onit causing the pure copper to pit and the great sensitivity of purecopper to work hardening when cold worked.

The above mentioned application points out that this type of failure ofcopper roofing as constructed from thin sheets, commonly from 0.003 to0.03' inch in thickness, can be substancopper controlled amounts ofarsenic.

When arsenicis incorporated it has been found I that the surface of thecopper, after the patina -or other accumulated products of corrosion areremoved, is in an unpitted condition, any corrosion which has occurredbeing substantially uniformly distributed over its surface. Also it hasbeen found that the arsenic most markedly de-. creases the sensitivityof the copper to work hardening when cold Worked, and therefore anyscratches, dents, or the like in the nature of notches which might beformed during the handling or installation of the roofing will not causeit to fail by notch effect. In other words, the action of the arsenic istwofold: it prevents notches from bein formed by corrosion and preventsthe roofing failing by notch effect even if the notches are accidentallyformed by mechanical means.

It has been found that the presence of the proper amount of arsenic inthe copper roofing produces on the roofing surface a corrosion filmwhich is tenacious, adherent, impervious and non-hygroscopic, the filmbeing comparably as ductil as the copper base material itself, thuspermitting the roofing to be repeatedly bent without ruptureof the filmor interruption of its adherence to the copper. Thus this filmeffectively protects the underlying base material from contaminated airand moisture, and in this way efiectivel-y eliminates the possibility ofthe formation of the above mentioned notch-like pits, for any slightamount of corrosion which occurs will be uniformly distributed over thesurface of the copper. Most importantly this film has the property ofbeing self-healing in the sense that if for any reason its continuity islocally interrupted it will substantially immediately reform whensubjected to corrosion and thus act to prevent substantial localcorrosion 'at the interrupted regions which in a pure copper wouldcontinue to corrode at an accelerated rate resulting in pitting at thepoint of interruption of thefilm. L

The above mentioned application points out that the beneficial effectsof arsenic in copper roofing are obtained with additions of 0.02 to 1.5%arsenic, the maximum beneficial effects being secured with about 0.05%.Applicant has now found that, in place of adding arsenic to the copper,the same and improved beneficial effects may be secured by addingcontrolled amounts of antimony.

Antimony, it has been found, causes the formation on the exposedcopper'roofing surface, of a corrosion film, consisting predominantly ofantimony content compound, having substantially the same physical andchemical properties as the hereinbefore described film which forms whenarsenic is added to the copper, this film caused by the addition ofantimony forming substantially immediately when the copper roofingsurface is exposed to contaminated air, mois-" ture, or other corrosivemedia, and being selfhealing in the same sense as the film formed whenarsenic is added. It further, like arsenic, reduces the sensitivity ofthe copper roofing to work hardening, and because of this and because itcauses the formation of the above mentioned film antimony, like arsenic,substantially prevents the possibility of failure of the roofing bynotch effect. Antimony, however, to a much greater degree than arsenicsecures a marked increase in the tensile strength of the copperAppreciable effects will be secured with as little as 0.05% antimony.The beneficial eflects increase with an increase in the antimony up toabout 0.8%, above which value the antimony tends to cause the copper tobecome cold short in'the sense that cold working either duringfabrication or when subjected to cyclic stresses after installationtends to form therein minute surface cracks analogous to notches. Whendeoxidized copper is employed, the antimony exists in thecopper-antimony alloyin solid solution with the copper. With coppercontaining oxygen it exists in the copper-antimony alloy for the mostpart in the form of a secondary phase which apparently consists ofcopper, antimony and oxygen, the remainder being in solid solution withthe copper. The effect of the antimony in either case however is thesame in respect to the properties hereinbefore mentioned, and for thisreason the much less expensive copper containing oxygen is preferablyemployed.

When adding antimony best results ordinarily will be secured when theroofing does not contain impurities which tend to render it lessmalleable in the hot and cold conditions and thus tend to cause the hotor cold rolling or other working of the roofing during its fabricationto result in submicroscopic surface cracks therein analogous in theireffects to pits.

Among these deleterious substances are lead, bismuth, iron, nickel andsulphur, very small amounts of all of which tend to make the copperroofing more dimcult to produce, and all of which tend to make theantimony bearing copper roofing approach the poor resistance of purecopper roofing to corrosion and its sensitivity to notch effect, andthereby act to destroy the beneficial effects of the antimony. Thepresence of such substances as cobalt, tin, silicon and zinc insubstantial amounts had also best be avoided .as they tend to increasethe sensitivity of the copper roofing to work hardening and notcheffect. Thus it willbe understood, that in the sense the copper roofingdoes not contain deleterious substances or amounts thereof whichsubstantially destroy the beneficial effects tended to be imparted bythe antimony, the balance of the alloy aside from the antimony isessentially copper.

W In making the roofing according to the invention the copper may bemelted, and the antimony added to the melt in the form of acopper-antimony alloy rich in antimony. The molten metal may then becast into slabs, which latter may be rolled into sheets of desiredthickness by the usual mill process of rolling copper roofing sheets.Finally the rolled sheets are annealed to the degree of softness thatwill best resist the cyclic stresses to which they are subjected when inuse. For convenience in terminology the article of manufacture accordingto the invention is termed roofing," it being understood that as used inthe appended claims such term includes various shingles, sheatings,valleys, and like protective coverings for buildings, as well as what ina more limited sense is ordinarly termed "roofhaving an exterior sheetof copper as well as consist wholly of sheet copper.

I claim:

1. Roofing comprising sheet copper presenting an extensive externalroofing surface, the copper being alloyed with such amount of antimonybetween 0.05 and 0.8% as will cause the formation on said surface whenexposed to atmospheric corrosion of a self-healing, adherent. protectivefilm composed predominantly of antimony content compound, whilerendering the sheet copper less sensitive to failure by reason of notcheffect than sheet copper without the antimony when subjected to thecyclic stresses caused by expansion and contraction of the roofing.

2. Roofing comprising sheet copper presenting an extensive externalroofing surface, the copper being alloyed with approximately 0.05 to0.8% antimony, the balance of the alloy in respect to the antimony beingessentially copper.

RICHARD A. WILKINS.

